The invention relates to a flame retardant thermoplastic molding composition based on an acrylonitrile-butadiene-styrene polymer (ABS), a copolymer matrix and a particular flame retardant component, where the flame retardant component comprises a phosphor-containing component (e.g. a triphenylphospin-compound), an expandable graphite component and a fluorinated polymer.
The invention further relates to a process for preparation of a flame retardant thermoplastic ABS molding composition and to its uses. The invention also relates to products such as moldings, foils and coatings, which can be produced from flame retardant thermoplastic molding compositions, and also to the uses of the molding composition. Instead of ABS as a component, a classical ASA-copolymer based on an alkylacrylate and styrene can also be used.
It has been known for decades that various thermoplastic molding compositions can be prepared by modifying styrene-acrylonitrile copolymers via incorporation of rubbers. By way of example, this is achieved via graft copolymerization of styrene and acrylonitrile in the presence of a rubber, and also via subsequent blending of this graft copolymer with a separately prepared polymer matrix which can, for example, be composed of a styrene-acrylonitrile copolymer and/or of a methylstyrene-acrylonitrile copolymer.
In the last years, various flame retardant components have been described. For example, in EP-A 0 730 000 a flame retardant polymer composition is described which can be used for various polymer compositions comprising a heat-expandable graphite and a phosphorous compound. However, most flame retardant compounds are not sufficient effective with polymers such as ABS and ASA. In EP-A 0 730 000 no fluorinated polymer is used in the polymer compositions.
In WO 2005/103 136, a fire retardant polymer composition is described which contains heat-expandable graphite and a phosphorous containing fire retardant. Furthermore, the compositions disclosed contain a co-additive to depress the migration of phosphorous containing retardants on the polymer surface. As this co-additive, a polycarbonate based on bisphenol A is used.
In EP-A 1 619 345, thermoplastic polymer materials are disclosed which contain as a flame retardant compound an ammonium phosphate compound and/or a graphite component.
However, no fluorinated polymers are used as further component in the thermoplastic moldings.
In WO 2006/058731, the combination of various polystyrole polymers with phosphorous compounds is described.
It also has been known for years that certain additives (e.g. zinkborate or expandable graphite) to polymer compositions can improve the flammability of the polymer product. For several polymers like e.g. polyamides or polyolefines, these flame retardant additives are described in the literature. However, for ABS-copolymers, no adequate flame protection is known without using components which contain chlorine and/or bromine.
The flame protection of the ABS-copolymer has a high economical need and should be achieved by mixing the copolymer components with the flame retardant components in a simple to be applied process.
The flame retardant component should help to avoid the polymer to burn even at direct contact with a flame and at higher temperatures. Furthermore, the melting and/or softening of the thermoplastic polymer should be reduced and the burning of polymer, and in particular polymer drops should be avoided. Polymer materials are desired to be flame-retardant to prevent fire accidents or fire spreading in use for e.g. insulating materials such as electric wires and cables; sheath materials; enclosures and internal parts of electric, electronic, and office automation apparatuses; interior materials of vehicles; and building materials.
Many polymer materials for such uses, particularly for electric and electronic devices, are enforced to be fire retardant by legislation. For flame retardancy of polymer materials, known flame-retardant additives include halogen type fire-retardant additives, magnesium hydroxide, aluminum hydroxide, red phosphorus, and phosphorus compounds. These fire-retardant materials, however, are not perfect, and have several disadvantages.
The halogen type fire-retardant additives, which give a high level of fire retardancy (for example the commercial products UL-94V-0, V-1, or V-2) with a small amount of addition, generate soot or smoke in a larger amount on burning. Further, the halogen type fire-retardant additives emit acidic substances such as a hydrogen chloride by heat of processing or at the time of fire accident, which would cause corrosion of the machines for resin processing, or produce adverse effects on human health or apparatuses in the vicinity of a fire site.
Metal hydroxides as flame-retardant, component such as magnesium hydroxide and aluminium hydroxide, are required to be added to the resin in a larger amount. The addition thereof in a larger amount, e.g. from 35 to 50 percent by weight, will impair the mechanical strength, lightweight/density and other characteristics of the thermoplastic polymer.
It also has been known for years that phosphorus type fire-retardant additives, such as red phosphorus and phosphoric acid esters, are effective in a small amount for polyamides, polyesters, polyphenylene oxides and other plastics. However, they have shown to have less effect of flame retardancy for other polymers e.g. for styrene thermoplastics, such as ABS, HIPS and polystyrene.